【作者】 高波；

【导师】 杨敏官；

【作者基本信息】 江苏大学 ， 流体机械及工程， 2009， 博士

【摘要】 伴有盐析的两相流动现象普遍存在于相关工业生产部门的盐类溶液输运流程中,结盐会造成能源与资源的极大浪费,这是学术界和工程界迫切需要解决的难题。目前对盐析两相流动理论的研究仍处于探索之中,叶轮机械内部盐析流动机理尚未被揭示。在国家自然科学基金项目（No.50476068）及江苏省普通高校研究生培养创新工程项目（No.CX07B₀93z）的资助下,本文选择适用于盐类溶液输运的旋流式模型泵为研究对象,以具有典型盐析特性的硫酸钠过饱和溶液为输送介质,围绕盐析两相流动理论、旋流泵内盐析两相流动机理等问题进行了较为系统的研究,主要工作及取得的创新性成果如下:1、从分析盐析过程基本理论入手,详细阐述了晶体成核及生长、晶体颗粒输运等过程及其与流动的关系,研究认为:盐析进程中,过冷度（过饱和度）是盐析晶体晶核形成最直接的相变驱动力,非均相成核与碰撞成核是泵内盐析晶体成核的主导机制,且成核速率、成核后的晶体颗粒粒径与浓度分布受当地流动条件的制约。2、借鉴界面相理论的思想,首次提出并定义了邻界区概念,用以描述盐析层及其邻近区域特征,并将其划分为盐析界面层、吸附层和过渡层三部分,每一部分的结构与特性各不相同,在盐析过程中所起的作用也有差异;同时也对盐析层的内部结构及特性进行了分析,阐明了盐析层增长的数学处理方法及实验研究方法,由此提出研究泵内盐析进程时可建立“扬程—盐析时间”关系的设想。3、在上述研究基础上,采用双流体模型构建了比较符合实际的盐析流动物理模型,再利用流体力学方法建立了完整的盐析两相湍流流动方程组,给出了质量、动量、能量交换率及其它本构关系式,并采用k-ε-k_p模型对方程组进行封闭;在方程中计入因叶轮旋转而产生的离心力和科氏力等惯性力的作用,建立了叶轮机械中的盐析两相流方程组。4、提出引入粒数衡算模型（PBM）来描述泵内因盐析晶体颗粒间及颗粒与叶轮叶片或流道内壁间碰撞而产生的聚并、破碎等微观行为,并将其与宏观属性联系起来。研究表明用PBM-CFD的耦合方法可提高双流体模型的精度,对其应用于盐析流场计算的方法及存在的问题进行了分析,为盐析两相流动研究提供了一种新方法。5、基于Eulerian多相流模型和混合的RNG k-ε两方程湍流模型,采用滑移网格技术,对模型泵内的盐析两相流场进行了全流道、三维非定常计算,初步揭示了不同时刻、不同温度条件下泵内液相和盐析晶体颗粒相的运动特性及颗粒的迁移规律;根据颗粒浓度分布特点,推测泵内的盐析进程为:盐析层最初在压水室内壁及叶片工作面形成并不断增厚,最终堵塞流道。此外对泵送清水和盐溶液时的性能也进行了预测,并将结果与外特性试验数据对比。6、运用PIV在径向和轴向两种测量模式下对泵内不同外部条件下盐析两相流场进行了准三维测量,经图像后处理,获得了盐析晶体颗粒在叶轮内、无叶腔中及轴面上的速度矢量分布,实现了颗粒流场的可视化,更为直观地揭示了泵内盐析颗粒的运动规律。计算得到的颗粒运动规律与PIV实验结果基本一致,但在数值上与实验值存在一定差异。7、摸索了一套PDPA应用于叶轮机械内部盐析两相流场测量的有效方法,并对模型泵内盐析两相湍流流动进行了较细致和全面的测量,获得了盐析两相在无叶腔与叶轮内的湍流流动特性、盐析晶体颗粒粒径分布及浓度分布规律,并通过改变运行工况、输送介质温度、浓度等这些影响泵内盐析流动体系的主要参数,发现并详细分析了盐析流动随外部条件改变后的演化规律,基本掌握了无叶腔及叶轮内的盐析流动机理。本文的研究成果、研究方法在一定程度上可以推广应用于其它类型叶轮机械内的盐析流动的研究。更多还原

【Abstract】 The salt-out two-phase flow phenomenon exists widely in the salt solution transporting process in relative industrial domain departments.It is a difficult issue both in academic and project field that costs vast waste of energy and resource.At present,researches on the salt-out two-phase flow theory are still on exploration road, especially in the internal field of impeller machinery.Under the support of National Natural Science Fund（No.50476068） and Postgraduate Cultivation Innovation Project of Jiangsu Province（No.CX07B₀93z）,vortex model pump suitable for salt solution transporting is adopted as the study object,and sodium sulfate supersaturated solution with representative characteristics of salt-out as the conveying medium in this paper. Systematic study on salt-out two-phase flow theory and salt-out flow mechanism in the vortex pump has been done.The major works and achievements are as following.1.Based on the basic theories of salt-out process,detailed descriptions about crystal nucleation and growth,crystal particle transportation and the relation with flow conditions are given.It is concluded that supercooling（or supersaturated） is the direct driving force of phase change in the nucleation process.Heterogeneous and collision nucleation become dominant mechanisms during pump salt-out.Nucleation velocity,crystal particle size and concentration distribution are affected mostly by local flow conditions.2.The idea of interface phase theory is helpful for proposing and defining the near interface zone.It is divided into three parts to describe the salt-out layer and zones nearby,such as salt-out interface,adsorption and transition layer.Each part with various structures and features makes different functions on salt-out process.Analysis on internal characteristics of salt-out layer is also taken.Mathematical and experimental methods on the layer increasing are illuminated.An assumption on looking for "pump head-time" relation is proposed for pump salt-out research.3.According to the practical process,two-fluid model is used to set up the physical model of salt-out flow.Then the whole salt-out two-phase turbulent flow equations are established by fluid mechanics methods.Constitutive relations are also given,such as mass,momentum,energy and so on.Equation group is closed by k-ε-k_p model.In order to establish the mathematics model in impeller machinery, centrifugal and coriolis forces due to the impeller rotation are involved in the equations.4.Population Balance Model（PBM） is introduced to describe the particle microscopic behaviors of coalescence and breakage,relate to the macroscopic features as well.It shows that PBM-CFD coupling may improve the precision of two-fluid model.Ways and existing problems of application on salt-out flow flied calculation are discussed.It provides a new way for studying the salt-out two-phase flow.5.Based on the Eulerian multiphase model and mixture RNG k-εturbulent model,three dimensional unsteady turbulent salt-out flow field in the pump is simulated by moving mesh technique.It is a preliminary study on the movements both liquid and salt-out particle phases at different time and temperature conditions. According to the particle concentration distribution,the salt-out process in the pump can be proposed that salt-out layer may formed on the internal wall of pump chamber and pressure side of impeller at first,and thickening until blocked the whole passage finally.Performance prediction of the pump when transporting water and salt solution is also studied.Results are compared and analyzed with experimental data.6.The salt-out flow field is measured on three dimensions by Particle Image Velocimemter（PIV） via radial and axial two test models.After image processing, velocity distribution of crystal particles in the pump is obtained.Particle flow field is visualized to reveal the particle motion law intuitionally.Except for the numerical difference,computational results are basically consistent with PIV data.7.Phase Doppler Particle Anemometer（PDPA） is used to measure the salt-out flow field in the pump in detail and completely.An effective method is groped for impeller machinery internal flow measurement.Turbulent flow features,crystal particle size and number density distribution in the impeller and volute are obtained. Evolution rule of salt-out flow with different external conditions is found and analyzed via changing the major factors that affecting flow system,such as pump running condition,conveying medium temperature and concentration.The salt-out flow mechanism in the pump is basically grasped at last.Research achievements and methods from this paper can be extended and applied on the salt-out two-phase flow in other types of impeller machinery.更多还原